Along with the recent rapid progress in the development of clean energy techniques, progress has also been made regarding techniques seeking for an earth-friendly society through reduction of petroleum dependency, zero emissions, distribution of power-saving products and the like. Particularly, an item that has recently attracted attention is a secondary battery used for an electric vehicle, a high-capacity storage battery capable of supplying energy in case of an accidental disaster, a portable electronic device and the like. For example, a lead storage battery, an alkali storage battery, a lithium ion battery and the like are known.
Particularly, a decrease in size and weight and an increase in capacity are possible in a lithium ion battery that is a non-aqueous electrolytic solution secondary battery. Furthermore, due to excellent characteristics such as high output and high energy density, the lithium ion battery has been commercialized as a high-output power supply not only for an electric vehicle but also for an electric power tool, and the development of a material for a next-generation lithium ion battery is being actively carried out across the globe.
In addition, recently, a home energy management system (HEMS) has been developed as a collaboration of an energy technique and a house, and a system that manages the optimization of automatic control and electric power supply and demand by integrating information concerning home electricity such as smart home appliances, electric vehicles or solar power generation and a control system, and efficiently consumes energy has been attracting attention.
Meanwhile, LiCoO2 and LiMnO2 are generally used as an active material for a positive electrode material of a lithium ion battery in current use. However, since Co is eccentrically present in the earth, and is a rare resource, considering the large amount of Co necessary as a positive electrode material and the like, there are concerns that the manufacturing costs may increase in a case in which Co is used to produce a product and a stable supply may be difficult. Therefore, as an alternative positive electrode-active material of LiCoO2, research and development are being actively carried out regarding a positive electrode-active material such as LiMn2O4 having a spinel crystal structure, LiNi1/3Mn1/3CO1/3O2 having a ternary material composition, lithium iron oxide (LiFeO2) or lithium iron phosphate (LiFePO4) that is an iron-based compound.
Among the above-described positive electrode-active materials, LiFePO4 having an olivine structure has been attracting attention as a positive electrode-active material having no problems with not only safety but also resource and cost.
An olivine-based positive electrode-active material represented by LiFePO4 contains phosphorous as a constituent element and has a strong covalent bond with oxygen, and therefore, compared with a positive electrode-active material such as LiCoO2, there is no case in which oxygen is emitted at a high temperature, there is no concern of a risk of ignition due to the oxidation decomposition of an electrolytic solution, and the safety is excellent.
However, even in LiFePO4 having the above-described advantages, there is a problem of low electron conductivity. The reason for the low electron conductivity is considered to be slow diffusion of lithium ions in the electrode-active material derived from the structure and the low electron conducting property.
Therefore, as an electrode material having improved electron conductivity, for example, an electrode material for which a plurality of primary particles including a formula LixAyDzPO4 (here, A represents at least one selected from Cr, Mn, Fe, Co, Ni and Cu, D represents at least one selected from Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y and rare earth elements, 0<x≦2, 0<y≦1.5, and 0≦z≦1.5) is collected so as to produce secondary particles and an electron-conducting substance such as carbon is interposed between the primary particles and a manufacturing method therefor (PTL 1, 2 and the like), an electrode material in which a conductive carbonaceous material is uniformly deposited on the surface of a complex oxide containing a transition metal or a non-transition metal (PTL 3), a positive electrode material including a complex of LiFePO4 and carbon (PTL 4), a positive electrode-active material for which a lithium-containing phosphoric acid salt having an olivine structure is used (PTL 5), and the like have been proposed.
In addition, as an electrode material having high capacity and an excellent charging and discharging cycle, a positive electrode-active material in which at least one of sulfur (S), phosphorous (P) and fluorine (F) are agglomerated on the surfaces of complex oxide particles containing lithium (PTL 6), a manufacturing method for an active material in which an active material of a lithium secondary battery or Fe impurities in a raw material that composes an active material is removed using a magnetic force (PTL 7), and the like have been also proposed.